This invention relates generally to a product cutter utilizing a high-pressure fluid jet and, more particularly, to methods and apparatus for selectively interrupting the flow of a high-pressure fluid jet in cutting and etching applications.
High-speed fluid jets, typically but not exclusively water jets, have been used to cut food, paper, plastics, wood, and even metals and glass for years. Water and other fluid jet cutting technology provide many advantages over conventional cutting alternatives. For example, these advantages include improved safety and reduced maintenance because there are no cutting blades that need to be regularly sharpened or replaced, and reduced dust and other airborne particulate generation due to a narrow cutting stream and entrainment of particulates in the jet stream In addition, fluid jet cutting provides a quick, flexible, and clean cutting process.
In fluid jets, pressurized fluid is ejected from a small orifice to create a thin, high velocity jet of water or other fluid. When the fluid jet impinges on the target product, a thin slice of material is removed, typically without any appreciable amount of cutting fluid absorption into the product.
In many applications of water jet cutting, the desired cutting operations require precise high-speed interruption of the water jet. Generally, the greater the detail of the cutting operation, the faster the interruption of the jet must be in order to attain such detail. Also, the overall achievable speed of a cutting operation is frequently limited by the rate at which the high-speed stream can be controllably interrupted. In such applications, a higher rate of water stream interruption will reduce the overall product processing time required.
Various methods and apparatus are currently available to controllably interrupt a high-speed water jet. One such method of interruption is to use a linear actuator to insert an object between the high-speed water jet and the product. Typically, a pneumatic linear actuator forces a blocker pin into the path of the water jet to interrupt the flow of the cutting stream and a spring provides a retracting force for the blocker pin. Existing pneumatic blocker pin devices achieve closure times of 50-90 ms, and thereby limit the speed at which products may be cut by the water jet.
U.S. Pat. No. 4,693,153, issued to Wainwright et al., discloses another water jet interruption technique. When interruption of the high-speed water jet is desired, a second high-pressure fluid is directed at the object cutting jet so as to disperse the latter and impair its cutting properties. The device that controls the second fluid flow is similar to the plunger pin device. A solenoid device within the jet obstructer device controls the fluid flow from the jet obstructer device. An energized solenoid closes a plunger mechanism that is normally held in an open position by a spring. In the open position, the mechanism provides high-pressure fluid to interrupt the object-cutting water jet. Similar to the plunger pin device, this device also lacks the high-speed interruption capabilities necessary for cutting products as rapidly as may be desired.
International Patent Application No. WO 93/10950 discloses a valve for controlling a constantly running liquid cutting jet. A pneumatically-powered rotary cylinder 2 is attached to one end of and elongate plate 1 to rotate the opposite end of the plate in and out of the path of flow of the liquid cutting jet. However, the opening and closing times for this rotary plate are only slightly better than that of existing plunger pin devices. Also, the cutting jet only strikes one position on the plate requiring frequent replacement of the plate.
Pivoting pin interruption mechanisms are taught in U.S. Pat. No. 5,931,178 and No. 5,927,320, both issued to Pfarr et al. and owned by the assignee of the present application. The Pfarr et al. patents both disclose a water jet blocking device that utilizes a blocking pin having a first end attached to a rotary actuator and a second end disposed near a high-speed fluid jet. An actuator pivots the blocking pin about a center fulcrum, such that the second end of the blocking pin can be selectively swung to block the high-speed jet stream. The pivoting pin interruption mechanism overcomes many of the disadvantages of the prior art, while permitting faster activation times and a durable apparatus. However, further improvements in activation time and durability remain desirable. Accordingly, certain embodiments of the present invention provide advantages over previous devices or methods of controllably blocking high-speed fluid jets.
In accordance with the present invention, a high-speed fluid jet blocker for selectively blocking a high-speed fluid jet is provided. The jet blocker includes at least one electromagnet assembly having a selectively energizable coil such that energizing the coil will induce a magnetic field. The jet blocker further includes a blocking bar having an area of high magnetic permeability, the bar being pivotable to at least either an open position or a blocking position by application of the magnetic field generated by the coil upon the area of high magnetic permeability. When the blocking bar is in the open position, the blocking bar is disposed away from the high-speed fluid jet. When the blocking bar is in the blocking position, the blocking bar blockingly intersects the high-speed fluid jet.